Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quantas vezes a propulsão de combustível é cng?
 ###Tabelas: CREATE TABLE 180_nm (180_nm_id AUTO_INCREMENT PRIMARY KEY, Model Number VARCHAR, Frequency VARCHAR, L2 Cache VARCHAR, Mult VARCHAR, Voltage VARCHAR, Socket VARCHAR, Release Date VARCHAR, Part Number(s) VARCHAR) CREATE TABLE fleet (fleet_id AUTO_INCREMENT PRIMARY KEY, Order Year VARCHAR, Manufacturer VARCHAR, Model VARCHAR, Fleet Series (Quantity) VARCHAR, Powertrain (Engine/Transmission) VARCHAR, Fuel Propulsion VARCHAR) CREATE TABLE other_film_projects (other_film_projects_id AUTO_INCREMENT PRIMARY KEY, Year INT, English title VARCHAR, Original title VARCHAR, Country VARCHAR, Length VARCHAR, Participation as VARCHAR) CREATE TABLE belfast_and_northern_counties_railway_1848–1903__&__northern_counties_committee_1903–1949 (belfast_and_northern_counties_railway_1848–1903__&__northern_counties_committee_1903–1949_id AUTO_INCREMENT PRIMARY KEY, Class VARCHAR, Type VARCHAR, Fleet numbers VARCHAR, Quantity made INT, Manufacturer VARCHAR, Date made VARCHAR, Date withdrawn VARCHAR) CREATE TABLE list_of_counties (list_of_counties_id AUTO_INCREMENT PRIMARY KEY, County VARCHAR, Irish name VARCHAR, County town VARCHAR, Most populous city/town VARCHAR, Province VARCHAR, Region VARCHAR)  
SELECT COUNT Fleet Series (Quantity) FROM fleet WHERE Fuel Propulsion = CNG